This invention relates to vehicle bumpers and more particularly to energy absorbing vehicle bumpers that manage moderate impact forces without incurring damage to the vehicle bumper or to the vehicle to which it is attached.
An early approach to energy absorbing vehicle bumpers used a relatively stiff steel beam attached to the vehicle body structure by hydraulic shock absorbers. These shock absorbers collapsed to absorb the energy of bumper impact forces and then recovered to return the bumper to its original state and position. Such systems are generally regarded as being complicated, expensive and design restrictive.
Another known approach uses a relatively stiff steel beam rigidly attached to the vehicle body structure and an energy absorber in the form of a resilient foam pad attached to a face of the stiff steel beam. These systems require manufacture and attachment of resilient foam pads which is time consuming and costly
Still another known approach uses a molded structural beam of high strength plastic that is rigidly attached to the vehicle structure and that absorbs impact energy by resiliency of the beam itself.
One such system is disclosed in U.S. Pat. No. 4,941,701 granted to Norman S. Loren Jul. 17, 1990 for a vehicle bumper comprising an impact energy managing bumper structure made of injection molded plastic that is secured to column rails of the vehicle body structure. The bumper structure comprises a beam of generally C-shaped cross section that has channels, buckling columns, horizontal and vertical ribs and specially formed mounting portions for managing impact energy. The bumper structure may include additional energy management inserts or additional energy managing material such as plastic foam. Moreover, the beam may include hollow portions that increase its resistance to deformation and displacement thereby contributing to its ability to dissipate impact forces. While this system may be suitable for its intended purpose, it requires the molding of complicated shapes which is time consuming and costly.
Another such system approach is disclosed in the U.S. Pat. No. 5,096,243 granted to John C. Gembinski Mar. 17, 1992. The Gembinski bumper assembly comprises a rigid support member, a outer shell or skin and an energy absorbent material contained within a cavity between the rigid support member and the outer shell. The support member includes a plurality of elongated box sections which consist essentially of wrapped fiber having interstices filled with resin. More specifically a core member of low density foam filler such as styrene beads is wrapped with a high strength fiber such as carbon, Aramid, polyester, or glass fiber. The wrapped core material is disposed in a cavity of a reaction injection mold and resin, such as urethane, polyester, nylon, epoxy or acrylic is injected into the mold to fill the interstices of the porous reinforcement material to form a structural reaction injected (SRIM) beam. While this system may also be suitable for its intended purpose, it likewise requires the molding of complicated shapes which is time consuming and costly.